Allergy to cow's milk is a dominant food allergy in babies and young children. The allergic reaction to cow's milk is most prevalent in early childhood, with figures generally reported between about 2 and 6%, and gradually decreases into adulthood to an incidence of approximately 0.1-0.5%. (Cow's milk allergy ranks among the most pervasive of human food allergies, alongside allergies to egg, soy, wheat, peanuts, tree nuts, fish and shellfish in terms of prevalence.) The long-term prognosis for the majority of affected infants is good. Roughly 80 to 90% of infants exhibit allergy to cow's mile naturally acquiring tolerance to cow's milk by the age of 5 years. However, there remains a strong trend in infants who recover from an allergy to cow's mile to develop atopic symptoms later in life, such as asthma, hay fever, or dermatitis to inhalant allergens later in life. This phenomenon has been dubbed the so-called “atopic career” or “atopic march” and infant allergy to cow's milk appears to be an early indicator of atopy. See, for example, Crittenden, R. G. and Bennett, L. E. (December 2005) “Cow's Milk Allergy: A Complex Disorder,” J Am Coll Nutr 24(6):5825-5915.
Numerous milk proteins (beta-lactoglobulin among them) have been implicated in allergic responses to cow's milk and most of these allergen proteins have been shown to contain multiple allergenic epitopes. There is also considerable heterogeneity among allergic individuals for the particular proteins and epitopes to which they react. Further complicating a complete understanding of the allergy, the allergic reactions to cow's milk are driven by more than one immunological mechanism. Both the incidence and dominant allergic mechanisms change with age; IgE-mediated reactions are common in infancy, non-IgE-mediated reactions dominate in adults. Interestingly, the prevalence of self-diagnosed allergy to cow's milk is substantially higher than the incidence reported in blinded and controlled challenge trials, suggesting that a proportion of the population is unnecessarily avoiding dairy products (likely due to a confusion between milk allergies and lactose intolerance, an entirely different malady).
Beta-lactoglobulin (“BLG”) is the major whey protein of cow and sheep's milk. In fresh, raw cow's milk, it is present in a concentration of roughly 3 g/L. BLG is also present in many other mammalian species. However, humans are a notable exception; human milk does not contain BLG. Thus, BLG is one of the principal proteins in cow's milk responsible for the allergic response in humans. (The caseins are the other dominant class of protein allergens found in cow's milk.) BLG is the most potent of the allergens found in cow's milk and is responsible for approximately 9% of all diagnosed food allergies. Because BLG is a known allergen to humans, many countries require that food destined for human consumption be properly labeled to indicate that it contains BLG. For example, in Europe, Annex IIIa of Directive 2000/13/EC requires manufacturers to prove the presence or absence of β-lactoglobulin to ensure their labelling satisfies the requirements of the directive. Conventionally, food testing laboratories use enzyme linked immunosorbent assays (ELISA) to identify and to quantify BLG concentrations in food products.
Notably, BLG is a whey protein. Whey protein is a mixture of globular proteins isolated from whey, the liquid material created as a by-product of cheese production. Whey protein is commonly marketed and ingested as a dietary supplement, and various health claims have been attributed to it in the alternative medicine and body-building communities. The protein in cow's milk is roughly 20% whey protein and 80% casein. The whey protein fraction of cow's milk is typically about 65% BLG, 25% alpha-lactalbumin, 8% serum albumin, and the remainder minor immunoglobulins. Thus, a human who is allergic to milk due to the presence of BLG will also be allergic to foods containing any appreciable amount of whey protein. Whey proteins can be denatured by heat, but even heat-denatured whey can still cause allergies humans.
Whey protein is typically sold in three major forms: whey protein concentrate (WPC), whey protein isolate (WPI), and whey protein hydrolysate (WPH). These products differ by their level of purity and other processing parameters. WPC contains a small, but significant, level of fat, cholesterol, and lactose. WPC's are typically from about 29% to about 89% protein by weight. WPI is further processed to remove the fat and lactose. WPI is typically more than 90% protein by weight. WPH is a whey protein product in which the proteins have been predigested and partially hydrolyzed. Highly-hydrolyzed WPH may be less allergenic than other forms of whey proteins.
As noted above, food testing laboratories conventionally use an ELISA to test for and quantify BLG concentrations in food products. While ELISA's are very sensitive and accurate, they are also expensive and require specialized equipment to assemble and read. ELISAs also require enzymes, careful incubation times and temperatures, and wet-chemical processing to develop. Thus, ELISA's are not an ideal format for a fast and cheap method to detect and quantify BLG in foods. Insofar as a significant minority of humans are allergic to BLG, and not all jurisdictions require that food be labeled to indicate whether it contains BLG, there remains a long-felt and unmet need for a quick and easy method to analyze an unknown sample, especially an unknown sample destined for human consumption, to determine whether it contains BLG.